BIOLOGY, MARINE — MAYER. 117 



The observations made on Ocypoda do not indicate that it sees in the sense 

 that man does, but that it only reacts to different intensities of light. It de- 

 tects the approach of man much more easily when the sun shines than when 

 it is cloudy, and also more easily in the middle of the day than in the early 

 morning or evening. 



There occurs a compensator}^ movement of the eye-stalks when the normal 

 equilibrium of an individual is disturbed. Painting the eyes with shellac and 

 lampblack causes individuals to become more quiet and to sit with the body 

 closer to the ground, as has been observed by Prentiss. When in this condi- 

 tion they seem to be much more sensitive to vibrations. Cutting off the eyes 

 produces the same effect, but such operations do not prevent them from feed- 

 ing when food is put within reach of their chelae. The eyes are least sensi- 

 tive when the light stimuli come from above ; in fact, when the observer is 

 directly overhead they pay no attention to his movements. Experiments 

 performed so far do not indicate that Ocypoda is more sensitive to one color 

 than to another. 



The olfactory sense is developed to some extent, but is not keen, and such 

 substances as carbon bisulphide, formaldehyde, and ammonia apparently do 

 not affect the organs of smell to any considerable degree. 



The otocysts are undoubtedly equilibrating organs, and their removal pro- 

 duces a decided disturbance in the equilibrium of Ocypoda, both when it is 

 on land and when submerged in water. There is no evidence that these or- 

 gans have an auditory function, or that this crab reacts in any way to sound- 

 waves ; however, no experiments have been performed to determine if sounds 

 have any effect on other reflexes. 



A so-called "stridulating ridge" is present on the large chela in both male 

 and female. It consists of a ridge of tubercles extending across the inner 

 surface of the propodite, and is placed so that when the forceps are bent close 

 to the basal segment the ridge comes in contact with a projection on the 

 former. While the writer has never heard any sound produced by this ap- 

 paratus, he has, on several occasions, seen fighting individuals moving the 

 forceps back and forth with great speed against the basal segment. 



Ocypoda is quite sensitive to vibrations transmitted to any solid object 

 with which it is in contact, and it reacts sometimes by jumping, but more 

 frequently by a sudden lowering of the eye-stalks. It does not seem to react 

 to vibrations of air or water. 



Experiments devised to determine whether Ocypoda possesses memory 

 gave negative results, but as these were undertaken near the end of the 

 writer's stay at Loggerhead Key, they are not conclusive, and must be con- 

 tinued later. 



Prof. Herbert S. Jenning-s ptirsued studies of the behavior of vari- 

 ous actinians, corals, and echinoderms, this work being a continua- 

 tion of his well-known studies upon the behavior of unicellular or- 

 ganisms, wherein he has demonstrated that the method of trial and 

 error applies to behavior throughout the animal kingdom. His work 

 upon these metazoans was devoted to the important problem of the 

 modifiability of behavior, an understanding of which is essential be- 



